Hi everybody!

Yesterday, on July 24th, we started VK Cup 2015 Finals! During the day all participants of the competition successfully went to the St. Petersburg, those who got here earlier enjoyed a great trip over the roofs of this beautiful city. And now we are waiting for a practice round that will happen in a few hours, giving participants an option to test their contest environment and do their best while solving several usual (and not only usual) problems. After the lunch, contestants will compete in the first round of the Finals that is called CodeGame Coding, where they have to write the strategy for a battle wizard.

During today and tomorrow not all of the Codeforces features will be available. On this weekend you may take a rest from writing contests and enjoy the results of the one of the biggest competitions of 2015.

The results of the practice round will be available for spectators by this link. Stay tuned!

Good day for all!

I invite you to participiate in the Codeforces round 313, which is prepeared by me and tunyash. Each of us is prepared four rounds then it is our fifth of ninth round to your notice. I figured out almost all problems (except D div.1), wrote the statements and analysis of all the problems, and tunyash has developed all problems.

Gerald is not coordinator yet and you probobly missed him. In this round you will meet him again and help him in his ordinary life problems.

I want to thank Zlobober, our translator Maria Belova (Delinur) and MikeMirzayanov and all Codeforces team for this platform.

This round will be held in unusual time — 17:00 Moscow Time.

Contest finished! Welcome to editoral:
Short editoral.
Extended editoral.

Div.1 scoring distribution:

500 — 1000 — 1500 — 2250 — 2250

Div.2 scoring distribution:

500 — 1000 — 1500 — 2000 — 2500

I wish you to enjoy solving problems!

Congratulations to winners!

Div. 1:
1. jqdai0815
2. qwerty787788
3. SirShokoladina
4. ainu7
5. Endagorion

Div. 2:
1. goons_will_rule
2. lbn187
3. crawling
4. loveannie
5. Jagabee

I would like to recommend Marathon 24, an annual team programming competition — I have participated in the first two editions and I had lots of fun. Problem writers are also welcome, details are given below.

Hello everyone!

Marathon24 is getting the contest ready for its third edition this fall (online qualifying round on October 17, 2015; and the Grand Final in Warsaw on November 28-29, 2015)!

Meanwhile, we are looking for support in preparing the tasks. We have two types of tasks — in the qualifying round we have optimization and algorithmic problems, each with 10 tests. In the finals there are game-like problems divided into rounds, which require building a strategy, observing the opponents’ moves and being alert for the whole 24 hours of the contest.

Here you can find the problem statements from previous editions of Marathon24: http://www.marathon24.com/archive/#2014-qualifications http://www.marathon24.com/archive/#2013-qualifications

We are also looking for tasks for the qualifyng round and task concepts for the finals. If you have an interesting idea for the task and want to prepare it for Marathon24 — contact us!

Any questions, doubts, suggestions? We’ll be more than happy to answer!

Send us an email to [email protected] and become a contributor to Marathon24! We are waiting for your ideas till Thursday, July 23, 2015.

For more information about the Marathon24 contest, please visit: http://www.marathon24.com.

Hello everyone!

Not so long ago summer trainings finished in Saratov State University, and to make it easier to monitor the success of our programmers we introduced a feature to add custom ratings. Now you also have this opportunity!

Currently rating is calculated as follows: overall rating is equal to the arithmetic mean of the ratings for each contest in which the user has participated. Contest rating depends on the ratio of problems solved by user and a number of problems solved by winner, as well as user's place in the contest. Also points for upsolving are added to the contest rating. There is a rumor that such method of calculating rating first was used in ITMO. More formally:

where

• R — contest rating,
• n — maximum of 50 and number of contest participants,
• place — 1-indexed used's place in the contest,
• solved — number of solved problems by the user,
• maxSolved — number of solved problems by the winner,
• upsolved — number of upsolved problems by the user,
• problemCount — total number of problems in the contest.

If a user participated in a team, his place equals to the place of the team in this contest.

To create a custom rating in the group you have to be its manager. There can be multiple ratings in one group with different sets of contests. There is a special button to create a rating in the group sidebar:

If you press the button rating creation form will appear:

Users are added to the rating only if they have participated at least in the given percent of all contests of this rating. By default one have to participate in 50% of all the contests.

If you wish you can set rating freeze date: upsolving after that date will not affect the rating.

Also now you can view status in groups: it shows only submissions for the group contests.

Good luck with training in Codeforces groups!

Hello Codeforces!

I'd like to invite you to Codeforces Round #312 (Div. 2). It'll be held on Tuesday, July 14th at 18:00 MSK.(notice the unusual starting time) and as usual Div. 1 participants can take part out of competition.

This is my second round after Codeforces Round 287 (Div. 2). :)

Great thanks to Maxim Akhmedov (Zlobober) for his great help in preparing the contest, Maria Belova (Delinur) for translating the statements into Russian, Mike Mirzayanov (MikeMirzayanov) for the great Polygon platform and Polygon's developers team for their hard work in enhancing Polygon system.

The scoring distribution will be announced later.

Good luck everyone and I hope you'll find the problems interesting. ;)

UPD1 Scoring distribution will be 500-1000-1500-2250-2500.

UPD2 Contest is delayed 10 mins. Sorry for inconvenience.

UPD3 Contest is finished. Thank you everyone!

UPD4 System testing finished. Congratulations to the winners.

You can find the editorial here.

Hi all, we participated in challenge24 as aimfund team (zeliboba, ArtDitel,Zhukov_Dmitry), took 6th place and here is my writeup. We really love challenge24 and 24-hour format, thank you guys for making it, and we are waiting for the next year. But I should say that writeup will be mostly negative because of overall impression.

UPD Psyho's 1st place writeup with solutions: http://codeforces.com/blog/entry/19023

Hello, Codeforces!

Previously, my contribution to the development of Codeforces was limited only by rounds preparation (Codeforces Round 288 (Div. 2), Codeforces Round 293 (Div. 2), Codeforces Round 297 (Div. 2)). But a month ago, I joined the wonderful Codeforces team led by Mike Mirzayanov (MikeMirzayanov). Traditionally, to understand all the niceties of this project, my work begun from Polygon system. I would like to tell you about its changes.

Polygon is a system for the preparation of programming problems. All Codeforces rounds and many other olympiads prepared in Polygon. Everyone at any time can use this system.

To edit the files in Polygon now used Ace Editor. It has a nice looking syntax highlighting and autocompletion (you have to press Ctrl + Space). Soon planned to implement this editor in Codeforces.